1. Field of the Invention
This invention relates to an optical encoder which detects relative displacement.
2. Description of the Related Art
To control, for example, a manipulator, a robot arm, or the like with high accuracy, it is necessary to incorporate a plurality of encoders acting as position sensors into each of the joints of the manipulator or robot arm. This configuration, however, causes the problem of increasing the size of the apparatus.
Specifically, when as many signal processing circuits for processing encoder signals as are needed are simply provided, a large space for accommodating them must be secured, which exerts an adverse effect on manufacturing cost.
To overcome the problems, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-139967 discloses the signal processing circuit of an incremental encoder where a plurality of position sensors output signals differing in phase. The signal processing circuit is characterized by including input process switching means for taking in output signals from a plurality of position sensors, selecting a signal to be processed from the output signals, and switching to the selected signal.
Specifically, Jpn. Pat. Appln. KOKAI Publication No. 7-139967 discloses a signal processing circuit which processes the output signals from a plurality of encoders that output analog-voltage encoder signals. That is, the output signals from a plurality of encoders acting as position sensors are input to the signal processing circuit. On the basis of a timing instruction created in the signal processing circuit, the signal processing circuit switches signals to be processed and processes the individual encoder signals. Jpn. Pat. Appln. KOKAI Publication No. 7-139967 has also disclosed a signal processing circuit which has a so-called multiplexer function (the function of sample-holding the signals from a plurality of encoders acting as position sensors in the signal processing circuit and processing the signals, switching them).
With the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-139967, the signals output from a plurality of encoder heads can be processed by a single signal processing circuit.
When a plurality of encoders are incorporated into, for example, a manipulator, a robot arm, or the like, the number of power supplies and the number of signal transmission lines are enormous. Accordingly, a space which accommodates the wiring lines must be very large. Moreover, the stress applied to the lines when the joints are bent must be reduced and an actuator which has a torque surpassing the stress is needed.
When many encoders are particularly provided to cope with the above problems, it is desirable that the power supply lines and signal lines should be combined into common lines to decrease the number of lines and save a space. Furthermore, with the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-139967, neither a sufficient reduction in the number of lines nor space saving can be realized.